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  #1  
Old 12-25-2018, 02:05 PM
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Not MB - GM 10si alternator conversion

All, I recently bought a cheap old Rolls Royce shadow (actually traded it for a cheap old W123 300D). It has a blown alternator that shorts and smokes as soon as you connect the battery. A common conversion is a GM 10SI alternator.

The Rolls Royce has an external voltage regulator in the trunk of the car which has me concerned. From what I see WRT to the wiring on under the hood. There's a big wire for the charging with a smaller wire attached which I can assume can be connected to pin 2 on the 10SI to regulate the voltage. There is also a secondary set of wiring which I assume are for the generator light that I may keep disconnected.

What i'd like to understand is whether i should wire new cables from the battery (which is also in the boot) or if i could use the existing wiring and what to do with the voltage regulator?

Thanks
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  #2  
Old 12-25-2018, 08:03 PM
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I assume that this is a Lucas 11AC setup or did it start life as a generator system? I have extensive experience with old Lucas systems and can help. You may also have a 3AW warning light assimilator, either on the firewall or maybe behind the driver kickpanel.

The 10SI is internally regulated, so the trunk mounted VR would do nothing after conversion. Aside from the large B+ lead, there are two 1/4" terminals, labeled 1 and 2. The "1" lead is D+, and the "2" lead is voltage sense. The "1" lead must be used to ground the panel light, as it supplies bootstrap current to the field. The 2 lead can usually be attached directly to the big B+ terminal, but if you find that charge voltage is inadequate, you would need to run it back to the rear of the car for voltage sense.

I can show you how to do all this, but again, you'll need to post some photos. I'll need a photo of that VR to identify it, and I'll also need a photo of the rear of the old alternator. Year of the RR would also help.

Last edited by Mxfrank; 12-25-2018 at 08:31 PM.
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  #3  
Old 12-26-2018, 06:59 PM
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Location: Dallas, TX
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Thanks, my question primarily concerns the voltage regulator. It's somewhere in the back off the car. My question is that if I leave it disconnected on the alternator side (I assume that it may be connected to the battery somehow too), will it cause any damage. I don't need it with the 10si because it's internally regulated.

Thanks
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With best regards

Al

Check out the W114, W115 enthusiast website.
http://www.stroke8.org

http://www.w108.org

Join the Mercedes W108 group
http://autos.groups.yahoo.com/group/mercedesw108/

My 280SL restoration

http://www.w108.org/gallery/albums/a...0959.thumb.jpg
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  #4  
Old 12-26-2018, 10:24 PM
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Again, it would be helpful to see a photo of the VR. Lucas VR's are what's called A-circuit, which means they regulate the field ground. If it's an 11AC system as I suspect, the VR will have a switched positive lead, a ground and an F- lead, which connects back to the alternator. Some of them also have a sense lead. You wouldn't need the F- lead at all, and nothing else would be functional unless F- was connected. The safe thing to do would be to disconnect the leads, tie them off and tape them. But I confess that in Jaguar applications, where the VR is front and center in the engine compartment, I leave the connector in place on the VR, and just disconnect the F- at the alternator.


The question is how you will get the dash light to work, and how you will get D+ to the alternator (actually, that's one question). Again assuming it's an 11AC, the light is operated by an assimilator...a thermal relay...which controls ground. The assimilator's heater is powered by ac current drawn directly from the alternator stator, before rectification. It's a very odd setup. You would need to bridge out the assimilator and ground the lamp to the 1 terminal on the alternator. Here's a diagram showing how I do it with an internally regulated Bosch alternator in a Jag application:


https://www.coolcatcorp.com/faqs/Boschwiring2.jpg
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